SEOUL — Secretive North Korea raised its military alert ahead of a live-fire artillery drill by rival South Korea Monday amid heightened tension on the peninsula during a delicate transition of power in the impoverished North.

The exercise, involving the use of mortars, some 5,000 rounds of ammunition and attack helicopters, took place near a disputed sea border off the west coast and near a South Korean island bombarded by the North after a similar drill in 2010.

South Korea said the drill, the second of its kind in the area this year, was routine and had passed without incident.

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“The exercise took place normally according to plan. North Korea maintained a higher level of response posture than normal,” the South’s Yonhap news agency quoted a military official as saying.

The North’s new young leader, Kim Jong-un, has taken a militaristic line in what analysts say is clearly an attempt to woo the backing of the powerful army as he tries to cement his grip on power as the third generation of the Kim dynasty.

Pyongyang had threatened “merciless retaliatory strikes” if the South violated its territorial waters during the exercise.

In its warning, North Korea said the South “should not forget” its shelling on the southern island of Yeonpyeong in November 2010, in which four people including two civilians were killed.

The attack on the island was the first on civilians since the end of the 1950-53 Korean War. The North at the time said the South’s military drill near the disputed maritime border triggered the bombardment.

The two sides are technically still at war having signed only a truce, not a peace treaty, to end the 1950-53 conflict.

North Korea, angered by what it says was Seoul’s disrespectful response to leader Kim Jong-il’s death in December, has unleashed a wave vitriol against its neighbour and vowed not to deal with the conservative government in Seoul.

North Korea’s ruling Workers’ Party is expected to formalize Kim’s rule at a special conference in April.

Since his father’s death, Kim has assumed the title of “supreme commander” and has focused on shoring up support from the military. Analysts say Kim, who is believed to be in his late 20s, now needs the party’s backing to keep North Korea stable and to expand his power base.

The conference could confer key party posts on the young Kim, such as a general secretary and chairman of the Central Military Commission, experts say.

Moon Chung-in of Yonsei University said the party had been resuscitated in the later years of Kim Jong-il’s leadership.

“The party now has more power and influence,” he said. “There is speculation that under Kim Jong-un there will be a more normalized pattern of governance around the party.”

Beijing, the North’s main ally and benefactor, has endorsed the succession process, while Seoul and Washington have stated they wish only for a smooth a transition of power. Regional powers are pushing for dialogue.

Washington hopes to clarify whether Pyongyang’s new leadership is willing to curb its nuclear program when U.S. and North Korean officials meet in Beijing this week.

Analysts expect little progress at Thursday’s meeting, the third between the two sides in the last eight months. They say the North will also likely seek food aid.